Method and arrangement for operating a wind turbine taking into account power losses

Abstract

A method for operating a wind turbine is proposed. The wind turbine has a rotor, a wind turbine converter and a wind turbine output terminal connected to a utility grid. The converter has a converter output terminal upstream of the wind turbine output terminal. An input signal related to an action output of the wind turbine is obtained at a location between the rotor and the wind turbine output terminal. A power difference is estimated between the power associated with the action output at the location and the output power at the converter output terminal. The converter is controlled based on the input signal and the estimated power difference.

1 . A method for operating a wind turbine having a rotor and a wind turbine output terminal connected to a utility grid, comprising:
 obtaining an input signal related to an action output of the wind turbine at a location between the rotor and the wind turbine output terminal;   estimating a power from the input signal;   controlling the wind turbine based on the input signal and the estimated power,   wherein the wind turbine has a wind turbine converter having a converter output terminal upstream of the wind turbine output terminal,   wherein the estimating the power comprises estimating a power difference associated with the action output at the location and an output power at the converter output terminal, and   wherein the controlling the wind turbine comprises controlling the wind turbine based on the input signal and the estimated power difference.   
     
     
         2 . The method according to  claim 1 , wherein the obtaining the input signal comprises:
 obtaining a first input signal related to an action output of the wind turbine at a first location, wherein the first location is between the rotor and the converter output terminal;   obtaining a second input signal related to an action output of the wind turbine at a second location, wherein the second location is between the converter output terminal and the wind turbine output terminal,   wherein the estimating the power difference comprises:
 estimating a first power reduction associated to transferring the action output at the first location to the converter output terminal; 
 estimating a second power reduction associated to a consumption of energy by a wind turbine component connected at the converter output terminal, and 
   wherein the controlling the converter comprises:
 controlling the converter based on the first input signal and/or the second input signal and the first estimated power reduction and/or the second estimated power reduction, and 
   wherein the estimating the second power reduction comprises considering an operational state of an energy consuming wind turbine component.   
     
     
         3 . The method according to  claim 2 , wherein the operational state changes from a high energy consuming state to a low energy consuming state or vice versa. 
     
     
         4 . The method according to  claim 2 , further comprising:
 obtaining an operational state signal of the operational state of the energy consuming wind turbine component, and   wherein the estimating the second power reduction is based on the operational state signal.   
     
     
         5 . The method according to  claim 4 , wherein the operational state signal is one of a binary signal and a signal varying linearly with energy consumed by the energy consuming wind turbine component. 
     
     
         6 . The method according to  claim 2 ,
 wherein a wind turbine component is arranged between the rotor and the converter, wherein the wind turbine component comprises a drive train mechanically connected to the rotor, a generator mechanically connected to the drive train, a AC-DC-AC converter electrically connected to the generator, and   wherein the estimating the first power reduction comprises estimating a component power loss associated with the wind turbine component.   
     
     
         7 . The method according to  claim 2 , wherein the estimating the first power reduction comprises estimating a component power loss of a wind turbine component, and wherein the component power loss is estimated as a function of a temperature difference between the wind turbine component and a surrounding of the wind turbine component according to:
   loss_component=constant*( T _component− T _surrounding),
   wherein:
 loss_component is the component power loss, 
 T_component is temperature of the wind turbine component, and 
 T_surrounding is temperature of the surrounding of the wind turbine component. 
   
     
     
         8 . The method according to  claim 2 , wherein the estimating the first power reduction comprises estimating a generator power loss of a generator of the wind turbine, and wherein the generator power loss is estimated as a function of a temperature of the generator and an electric current flowing through the generator according to:
   loss_generator= c 0+ I   2 *( c 1* T+c 2),   wherein:
 loss_generator is the generator power loss, 
 c0, c1, c2 are constants, 
 I is the electrical current flowing through the generator, and 
 T is the temperature of the generator. 
   
     
     
         9 . The method according to  claim 2 , wherein the controlling the converter comprises:
 deriving a reference signal of a reference power, and/or a reference torque, and/or a reference voltage based on the input signal and the estimated power difference, and   supplying the reference signal to the converter,   wherein the input signal comprises the first input signal and/or the second input signal, and   wherein the estimated power difference comprises the first power reduction and/or the second power reduction.   
     
     
         10 . The method according to  claim 9 , wherein the reference signal is derived based on a difference between an intended mechanical rotor power and the estimated first power reduction, and/or wherein the reference signal is derived based on a difference between a sum of power output at the wind turbine output terminal and the estimated second power reduction. 
     
     
         11 . The method according to  claim 9 , wherein the reference signal is further based on a wind speed. 
     
     
         12 . The method according to  claim 1 , wherein the controlling the wind turbine further comprises supplying a blade pitch signal to an actuator for adjusting a pitch angle of a rotor blade connected to the rotor. 
     
     
         13 . The method according to  claim 1 , further comprising operating the wind turbine subsequently in at least one of a first mode, a second mode, and a third mode, wherein the wind speed is:
 in a first interval in the first mode, and a rotational speed is below a rated rotational speed, and an intended rotor power is below a rated rotor power,   in a second interval in the second mode comprising a higher wind speed than the first interval, and the rotational speed is at the rated rotational speed, and the intended rotor power is below the rated rotor power, and   in a third interval in the third mode comprising a higher wind speed than the second interval, and the intended rotor power is at the rated rotor power.   
     
     
         14 . The method according to  claim 13 , wherein a pitch angle of a rotor blade of the wind turbine is fixed during the first mode, wherein the pitch angle is changed based on the intended rotor power and the wind speed in the second mode, and wherein the pitch angle is further adjusted to maintain the rated rotor power in the third mode. 
     
     
         15 . An arrangement for operating a wind turbine having a rotor, a wind turbine converter and a wind turbine output terminal connected to a utility grid, the converter having a converter output terminal upstream of the wind turbine output terminal, comprising:
 an input terminal for obtaining an input signal related to an action output of the wind turbine at a location between the rotor and the wind turbine output terminal; and   a processor adapted to:
 estimate a power difference associated with the action output at the location and an output power at the converter output terminal; and 
 control the converter based on the input signal and the estimated power difference.